The objective characterisation of ultrasonic carotid plaque features

To determine the influence of ultrasonic carotid plaque morphology on the incidence of ipsilateral hemispheric symptoms (IHS).

Cross-sectional study.

A consecutive series of 80 patients (96 plaques) with more than 50% ICA stenosis was studied.

B mode ultrasonic images were captured and transferred to a computer on magneto-optic disk and standardised using linear scaling so that adventitia would have a grey scale median (GSM) value of 185-195 and blood 0-5. The GSM and the percentage of echolucent pixels (PEP) in plaques were determined to measure echodensity. Homogeneity, entropy, and contrast were also determined to measure spatial distribution (heterogeneity) of grey shades in each plaque. Each measurement was correlated to presence or absence of IHS.

Twenty-five plaques were associated with IHS and 71 plaques were asymptomatic. In symptomatic plaques the mean of GSM was 23 and the mean of PEP was 70%, compared to 38 and 55% respectively in asymptomatic plaques (p = 0.02; Wilcoxon test). Sixty per cent of symptomatic plaques were associated with a homogeneity, entropy, and contrast values of > 0.2, < 2.95, < 150 respectively as compared to 40% in asymptomatic plaques. Multiple regression analysis revealed that the GSM and the PEP were the most significant variables (p = 0.001) that are related to presence or absence of IHS.

This study indicates that computer aided analysis of ultrasonic B mode features of carotid plaques could identify a potentially high-risk subgroup (patients with IHS). A GSM less than 40 or PEP greater than 50% is a good predictor of IHS related to carotid plaques. The fact that these measurements are operator independent and performed after image standardisation should encourage their use in multicenter clinical trials where different operators and equipment are used.